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Head First 2D Geometry by Dawn Griffiths, Stray

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Since the bases ar
e
para
llel, the angles
her
e are supplementary
…but w
e can’t w
ork out the
ar
ea of the tr
iangles because
we don’t know enough side
lengths.
int
o simpler s
hap
es…
trapezoids have only two parallel sides
There are some familiar things about
this shape
It’s a four-sided shape, but it only has one pair of parallel sides.
These parallel sides are called bases. We call this shape a
trapezoid.
T
he bases her
e
(r
emember y
our F, N,
and Z pa
tterns?).
are para
llel.
But what’s the area?
In theory, we could split the trapezoid into a rectangle and two
right triangles, and then add together the area of each shape. The
trouble is, we don’t have enough information to do this. We know
that they’re both right triangles, but we don’t know what the other
two angles are, and we only know the length of one of the sides. So
what can we do instead?
28 meters
A trapezoid
has exactly one
pair of opposite
parallel sides.
24 meters
53 meters
24 meters
W
e can spli
t the trapezoid
262 Chapter 6
quadrilaterals
Instead of splitting the shape up, let’s add to it and see if that
helps us figure out how to find the area of a trapezoid. Here are
two congruent trapezoids. Draw them together so that they form
a single parallelogram.
What’s the width of the parallelogram?
What’s the height of the parallelogram?
What ideas does this give you about how to calculate the area of a trapezoid?
you are here 4 263

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